I'm interested in pre-Viking and early viking mail. What would this have looked like? Would it be a full hauberk, or more of a byrnie? Basically, what would the sleeve length be like, and how far did the skirt go down?

No longer than elbow length in the arms, Waist/hip length for migration period getting gradually longer until it hits knee length (then a bit longer still when you go Norman sleeves appear to stay elbow length until Norman times). Some, but not all, shirts appear to be dagged around the bottom. (Now watch some-one who knows more than me get it right - or maybe just right-er )

What would be a good way to make the dagges (or whatever the proper term would be )? The basic idea of putting triangles on the bottom is easy enough, but what width/length would they be? And is it just the skirt, or would sleeves and/or the bottom of coifs be dagged as well?

On am unrelated note, I know some Roman mail would have bronze/brass rings along the edges, is that a tradition that would have been carried on?

The Normans (who were essentially Frenchified Vikings who took control of England) continued to produce and prescribe both long and short hauberks well into the 12th century and beyond for feudal levy troops, depending on their wealth. The Assize of Arms of 1181 makes a clear distinction (in the original Latin text) between a mail coat or haubercum and a mail shirt or albergellum; in 1194 a mail coat was valued at £2, a mail shirt at £1. Better quality mail coats might cost up to £5 - compare this with the price of a reasonable quality destrier/war horse: about £3.

In the early 13th century, the borough of Dunstable was obliged to provide 1 mail coat, 9 mail shirts and 12 padded aketons for the royal levy - Bartlett states that this ratio reflects the relative frequency of the different types of body protection among non-noble troops (England under the Norman and Angevin Kings).

I have never, actually, sat down down and looked at how many dags and what size......... I would guestimate that 8 - 12 individual triangles attached to the 'hem' of the shirt (so that their bases meet) and between 5 an 8 inches 'hem' to point. You could try making paper dags of different dimensions and trying them against the shirt to see which option looked best.